I am travelling from CDG-LHR in economy and am going to be definitely over my baggage allowance.

What are their excess baggage rates, their office is closed I tried to call hence im posting here. Eurostar as usual dont want any customers, so I have to wait till their offices to open to speak to a mostly dementend human being and try get a semi-reasonable fair that isnt vastly differential depending on which I claim to be from while booking, when attempting to book online.

I have an IB gold and AA plat card, however their respective websites say thez onlz afford me extra baggage when travelling on their airlines or will BA give me an extra 10kg.

Excess baggage is usually calculated at 1.5% per kg of the full one-way fare on your route, although some European destinations are, for reasons beyond my knowledge, calculated at 1.4%. To err on the side of caution, I would make any calculations based on 1.5% as I do not know which side of the fence Paris falls on.

The full Y class fare CDG-LHR is EUR370.00 before tax. 1.5% of this is 5.55, so excess baggage should be approximately EUR5.55 per kg.

Your IB and AA cards do not entitle you to a higher baggage allowance unfortunately. You will be at the mercy of check-in staff as to how rigourously they enforce the 23kg baggage allowance (or 30kg if you are Club Europe).